Gamete characteristics and early development of the hooded oyster Saccostrea cuccullata (Born, 1778)

Abstract

The hooded oyster, Saccostrea cuccullata (Born, 1778), is an important aquaculture species on the coast of Thailand. Its aquaculture is mainly based on wild seed collection, the availability of which is becoming unstable due to environmental changes and pollution. To support aquaculture of this species, seed production in the hatchery is therefore required. Unfortunately, information on seed production is not available in this species. Therefore, the aim of this work was to study gametes and early stage larval development in order to improve current knowledge of fertilization and larval development in this species. Spermatozoa and oocytes were collected from mature oysters by a strip spawning method and characterized under a light microscope and a transmission electron microscope (TEM). In vitro fertilization was performed in 30 ppt filtrate seawater to observe developmental stages until the D-larvae. Results showed that oocytes, when fertilized with spermatozoa, underwent meiosis I (15 min) and meiosis II (30 min), indicated by the presence of the first and second polar bodies, respectively. The first cleavage, holoblastic unequal type, occurred 50 min after fertilization. A polar lobe was observed during the first cleavage and fused with one of the two cells to form one small and one large macromere. The larvae then continuously developed to trochophore larvae over 8 h. D-larvae were observed 24 h after fertilization. Results obtained from this work improve current knowledge of gametes and early developmental biology of the larvae in this species. This knowledge is important for developing hatchery methods for S. cuccullata.